In recent years, we have had several total lunar eclipses during which the moon appeared red. This color of the moon during a total eclipse can actually change from copper to deep red depending on the conditions and content of the atmosphere.

First, the moon does not have any light of its own, it shines because its surface reflects sunlight. The reason why the moon takes on a reddish color is a phenomenon called Rayleigh scattering which is the same mechanism responsible for colorful sunrises, sunsets and for the sky to appear blue.

Second, sunlight, known as visible light looks white but is composed of colors of different wavelengths. The color violet has the shortest wavelength and from violet progressively get longer with indigo, blue, green, yellow, orange, to red. The colors in the red section of the light color spectrum have longer wavelengths and lower frequencies when compared to those colors on the violet section of the spectrum, which have shorter wavelengths and higher frequencies.

This Rayleigh scattering phenomena is associated with the earth′s atmosphere, which extends about fifty miles above the planet surface and contains different gases, water droplets, ice crystals, dust particles, pollutants and ash. The atmosphere allows sun light to pass through it, but not all of the colors all of the time due to some colors being scattered into different directions by the striking of these particles. Not all colors are scattered equally, and those with shortest wavelengths, such as violet and blue are scattered the most and do not make it to any color palette that shows up with the sunglow, suntouch and other colorful palettes.

At sunset, sunrise, and moon eclipses, the violet section of the light spectrum including the green, blue, indigo and violet colors are filtered out by the Rayleigh scattering, leaving the reddish portion of the light spectrum which is the least affected by the atmosphere. Rayleigh scattering happens when sunlight enters the earth′s atmosphere and strikes the particles that are smaller then the color′s wavelength.

In fact, red light upon entering the atmosphere is bent or refracted towards the earth and upon exiting the opposite side of the atmosphere, it′s bent again.

This double bending of the red light sends this color directly to the moon during a total lunar eclipse.

There are several things that can change the color, including dust, humidity, temperature and what we came to find out recently with all the fires in the northwestern portion of the American continent, is that forest fires can be a contributing factor for a red moon.

When sunlight strikes gas molecules, such as nitrogen and oxygen, light of longer wavelengths, like red, yellow, and orange, easily passes through, while light of shorter wavelengths, such as blue and violet, is absorbed and then scattered in all directions by the gas molecules.

When you look up at the sky during the day, this scattered blue and violet light reaches your eyes, however, the human eye is more receptive to blue frequencies than violet frequencies, so the sky looks blue.